Britain will deploy an extra 3,500 troops at the London Olympics after a private security firm said it could not provide sufficient guards, the defence minister confirmed on Thursday.
Philip Hammond said the interior minister Theresa May requested the move after private contractor G4S could not supply the promised number of trained staff for the Games, which officially open on July 27.
The deployment, which means 17,000 troops will now be involved in the Olympics, would impose an extra burden on the armed forces over the British summer holiday season, but was "prudent" to ensure security, Hammond said.
The extra deployment of 3,500 is equivalent in size to more than a third of the current total British military force of 9,500 in Afghanistan, but Hammond said it would have "no adverse impact on other operations."
"As the venue security exercise has got under way, concerns have arisen about the ability of G4S to deliver the required number of guards for all the venues within the timescales available," he said in a statement to lawmakers.
"G4S has now agreed that it would be prudent to deploy additional military support to provide greater reassurance.
"The home secretary has therefore requested additional Ministry of Defence support, and I have authorised the deployment of a further 3,500 military personnel."
The extra soldiers will work alongside police, private security guards and unpaid volunteers for a total security force of around 40,00 people at the London Olympics.
The government's security budget for the Games stands at £553 million ($877 million, 662 million euros).
Hammond said all soldiers involved would receive their full leave entitlement and compensation if they had had to change any arrangements.
A G4S spokeswoman admitted they had "encountered some issues in relation to workforce supply and scheduling" and had difficulties with processing applicants to be security guards.
It was unclear what would happen to the reported £300 million fee the government had paid it for Olympic security.
May told lawmakers that the government had built in contingency plans to what is Britain's largest security operation since World War II.
"We have deliberately built in flexibility to respond to any challenges," she said.
May said the government was now donating 10,000 Olympic and Paralympic tickets to the armed forces, as well as 7,000 tickets for dress rehearsals of the Olympics opening and closing ceremonies.
Meanwhile an independent watchdog warned that border staff drafted in to cope with the influx of visitors to Britain for the Games may lack proper training and immigration experience.
John Vine, chief inspector of borders and immigration, said extra staff brought in to ease congestion at Heathrow Airport, the main gateway to the Games, were taking longer to process visitors despite asking fewer questions.
In another pre-Games scare, Britain's Highways Agency on Wednesday said it expected the main road between Heathrow Airport and London to reopen in time for the Games despite ongoing repairs to a cracked viaduct.
The M4 motorway will be the main artery for transporting athletes and officials from Britain's busiest airport to the Olympics.